Gear-hobbing machine



Feb. 9, 1960 o. UFERT 2,924,151

GEAR-HOBBING MACHINE Filed DEC. 23, 1953 2 Sheets-Sheei 1 Feb. 9, 1960 o. UFERT GEAR-HOBBING MACHINE 2 Sheets-Sheet 2 Filed Dec. 23. 1953 INVENTO their teeth cut by gear-hobbing machines.

Unite States Patent ice Fe., 9, .0

2,924,151 GEAR-Hossain MACHINE Otto Ufert, Dusseldorf-Oberkassel, Germany, assignor to Schiess Aktiengesellschaft, Dusseldorf-Oberkassel, Germany Application December 23, 1953, Serial No. 399,967

Claims priority, application Germany December 23, 1952 2 Claims. (Cl. 90-4) The present invention relates to gear-cutting and, mo're specifically, to gear-bobbing machines.

Gears which have to meet the highest requirement as to precision as, for instance, gears of turbine drives which rotate at high circumferential velocities, have as a rule The reason for this consists in that this type of machine has the advantage over all other gear-cutting machines that during the gear-cutting operation, the workpiece as well as the cutting tool in addition to carrying out a yvery slow and,

steady feeding movement carry out only rotative movements but no reciprocating movements. This is of greatest importance with regard to the precision of the workpiece to be machined.

One of the most important prerequisites for the proper working of these machines consists in that the cutting tool and the workpiece perform an as synchronous movement as possible because with the least leading or lagging of the cutter movement with regard to the movement of the workpiece, gear-cutting errors will occur which ultimately will make the nished gears run rather noisily. The requirements as to precision are, therefore, frequently so high that already errors of a few arc seconds are considered inadmissible.

The greatest diiculty encountered in the eiort to' obtain a precisely synchronous movement of gear cutter and workpiece consists in that the workpiece together with the workpiece table offers a relatively uniform resistance during the movement thereof, whereas the gear cutter is periodically subjected to stroke-like greatly changing loads. For, whenever a tooth of the gear cutter enters into the workpiece, the resistance is increased almost instantly and drops or is reducedwith the same suddenness when a tooth of the gear cutter leaves the workpiece. In View of these load fluctuations, the cutter spindle, due to the elastic tensioning occurring during the cutting operation, has the tendency periodically to' jump forward or to lag depending on which phase of the periodically fluctuating resistance is involved at the respective time. This non-uniformity of the cutter movement is still further increased by the back lash in the cutter gears if such back lash is about to react upon the cutter spindle. This is above all the case if the cutter spindle is driven through the intervention of spur gears, because spur gears are unable to resist a springing forward of the cutter spindle. The braking devices which are frequently as auxiliary equipment associated with cutter spindles reduce this error somewhat but they are, by no means, an ideal means for preventing torsional vibrations of the cutter spindle because not only do they destroy effective driving forces and represent an additional load for the transmission shafts but they also bring about a warming up of the cutter spindle and thus in view of thermal stresses and thermal expansions bring about inaccuracies. Moreover the elastic tensions in the cutter spindle drive are so great that they cannot be sufficiently absorbed or intercepted by normally dimensioned braking means.

Therefore, ger-liobbing machines have been designed so that the drive o'f the cutter tool is effected through the intervention of a worm wheel mounted on the cutter spindle. In order to prevent an elastic jumping forward of the cutter spindle, there are as a rule two worms provided one of which brings about the drive, whereas the second is under load in axial direction with regard to the first one so that it rests against the oppositely located flanks of the worm wheel teeth and in this way brakes the rotation of the cutter. However, such an arrangement hardly produces more than the same eifect obtained when braking cutter spindles driven through the intervention of spur gears.

lt is, therefore, an object of the present invention to provide a gear-bobbing machine which will overcome the above mentioned drawbacks.

It is still another object of this invention to provide a gear-bobbing machine which will have a minimum of back lash in the driving elements and in which the driving shafts for the spindle drive will be as short as possible.

It is still another object of this invention to provide a gear-hobbing machine with which the unavoidable errors in the gear elements will only to a very minor effect affect the uniformity of the drive for the gear cutter in order in this way to pro'duce as precise a synchronous movement between gear cutter and workpiece as possible.

A still further object of this invention consists in the provision of a gear-bobbing ymachine as set forth in the preceding paragraph, in which the uniformity of the movement between workpiece and cutting tool will be assured during the forward as well as the backward movement of these elements without the necessity of employing special means for braking the cutting spindle.

These and other objects and advantages of the invention will appear more clearly from the following specification in connection with the accompanying drawings in which:

Fig. 1 illustrates a side view of a gear-hobbing machine according to the present invention.

Fig. 2 is atop view of the gear-hobbing machine shown in Fig. l.

Fig. 3 is a section taken along the line 3 3 of Fig. 1.

Fig. 4 is a section through the cutter spindle drive taken alo'ng the line 4-4 of Fig. 3.

Fig. 5 illustrates an end view of the lower worm wheel shown in Fig. 4 and seen in the direction of the arrow 5.

General arrangement The gear-bobbing machine according to the present invention in which the cutting tool is driven through the intervention of a worm wheel mounted on the cutting spindle, is characterized by two' worms which are arranged opposite each other and simultaneously drive the cutting spindle. The arrangement may be such that the two oppositely located worms mesh with the same worm wheel. l In this way a maximum in uniformity is obtained and additionally the conditions are created which make it possible to provide short shafts fo'r the cutter drive. In addition thereto, the bearing for the worm wheel is relieved from the driving tooth pressure so that it can be adjusted with a minimum of back lash. Thus Aerrors in the gearing of the worm wheel are prevented from having any harmful effect. 'Ihe two worms are advantageo'usly driven from a single shaft through gear trains of the same length. In this way, the elastic deformations in the branches of the cutter drive will be of the same type and of the same magnitude and a steady engagement or contact of the two worms and an even drive of the cutter spindle is assured from both sides.

According to a further development of the invention, the gear trains from the driving shaftto the cutter spindle are arranged symmetrically with regard to the` plane passing through the axes of the shaft and spindle.

A further feature of the invention consists in that each ofthe -wormsis connected with the drive shaft common to them merely through the intervention ofl one` gear. In this wayrthe gear` train is short and the harmful elasticity is reduced toa minimum.

Stillanother feature of the present invention. consists in that thef rightv and left flanks of each of-the two worms have different pitch and that both wormsV are axially as well as radially adjustable with regard to each other sotthat it is possible to cause-both worms to mesh with the worm wheel not only simultaneously` but also without back lash.

Structural arrangement Referringfnow to the drawings in detail and Figs. 1 and 2 thereof in particular, the workpiece w to be provided with teeth is fastened to the workpiece table t which latter is driven by a variable motor m inamanner known yper se through the intervention of theidividing dividing shaft d through a vertical shaft l and bevel gears i. Upon this shaft d there is mounted a spiral gear s- (Figs. 3 and 4) which simultaneously drives two wormv wheels c|1 and c2 located opposite to-each other@ Each of theseV worm wheel gears is adjustably connected with a worm' a1, a2, and' the two worms-a-l' and a2 simultaneously driven by the spiral gear s in their turn simultaneously drive a worm wheel e which is mounted `on the cutterspindle 'ony oppositely located sides off said worms, li.e. symmetrically'` with regard to the vertical plane pasing through the axes of the shaft d and spindle f. This bilateral drive results ina particularly effective increase in the uniformity of the cutter movement because lthe bearing of the worm wheel e is completely relieved from-the tooth pressure on the driving teeth'v of the Vworms a-l, a2, and errors in the gearing of the-worm wheel e will have their possible effect upon thecutter spindle 1" considerably reduced; Since the worm wheel e for conveyingthe same output can be vdesigned smaller than heretofore necessary, it is alsopo'ssible to design the'distance q of the worm' wheel e'up to the center line n (Fig. 3) smaller than heretofore customary. This distance is determined bythe diameter of tlie workpiece w and must be'ofsuch magnitude that the largest workpiece to be machined on-the machine will still pass by the casing of the worm wheel e. In view of the reduction of the diameter of the' worm wheel e and thusofthe distance q as made possible by the invention',- alsoi the distance from the worm'whee'l e up"4 to the cutter-center line andthelength of the shaft d isreduced-Which in turn further increases the uniformity of the rotation of:V the cutter.

The flanks r-1 and rZ- of the-twoworms a-1-, a2`f` respectively have the pitch Iz'r, whereas the lianks gelI and g2 of thetwo worms have" a` pitch hg differing from? the pitch hr. In view of thev difference between the: pitch hg and hr, also-the thickness of the screw threaldto-ffthe worms a-1 and a2 is changed aswill clearly be visible from Fig. 4. Byaxially adjusting the worms onthe worm shafts -1,.02 by means of nuts p, the two warmste-M412r each one by itself can becaused to mesh with the worm wheel e without anyback lash. The two worms all;A a2 may also be' adjusted relative' to each other with regard to the rotational positionthereof. To' this andy-through the intervention of an intermediate liange j-l' (Figs. 4 and-5) 'providedvwith arcuatefslotsi2, tieworm wheel c2 is connected withl thewo'rm-n'z sothat'by mere-loosen'- ing. of thetconnecting` screws i3 'adapted'l toV bel screwed into various'threaded bores jai, each desired rotational 4, position of the worm a2 with, regard. to the worm a-L can be obtained. This double adjustability of the worms a4, a2 with regard to their rotational as well as their axial position relative to the worm wheel e is of particular importance in connection with the thickness of the Vthread portions of the worms which thickness changes in view of the dierence between the pitch hg and hr, j

because in this way it is possible without,brakingdevices,`

brakes ori the like to obtain a drive of the worm wheel which is completely free from back lash, Thus,V rotational oscillations of the cutter spindle fare intercepted close to the points where such oscillations originateand, therefore, said oscillations are prevented from' ybeing conveyed backwards into the transmission.

The length of the kinematic chain from the spiral gear` s through the worm wheel c1 to the worm a-l is precisely as short as the length from the spiral `gears through the wormv wheel c2 to the worm a2'. Inthis way, there is assured not only" a continuously evenly` maintained drive of the worm wheel e fromboth" sides thereof in normal direction of rotation of worm wheele, but also in the` reverse direction. This is of particular importance when'cntting with left-handed cutters because in such an instance it is most frequently necessary to' re-` verse the directionl of rotation of the cutter.

Theinvention is not limited to the particular embodi-` vision of fly-wheel masses on the worm shaltso-l,` 02

without, in any way, affecting the present invention.

It is also to be understood that the present invention is, by no means, limited to the arrangements set` forth in the preceding description but also comprises any modications within the scope of the appended claims.

What I claim is:

1. In a gear hobbing machine having arotatable workpiece supporting table, guiding means forf al gear' cutter supporting slide, said guiding means being'- movable toward and away from said tab1e,1a`nd a gear' cutter supporting slide slidable on said guiding means andy including a cutter spindle for supporting and rotating a gear cutter, theV combination of: a worm'wheellrotatably connectedl' to saidv cutter spindle, two worms respectively arranged in meshing engagementwith saidi worm wheel and placed Vdiametrically opposite each othenisa'id worms being arranged simultaneously to impart driving force upon said worm wheel in one and the samewrot'ative direction of said worm wheel, means associated with said worms for effecting axial and circumferential adjustment of said worms, the right and left Hanks of'each. of said two worms having a different pitch, and driving means common to said worms and` arranged to drivef said worms simultaneously to `thereby cause both worms to rotate said worm wheel in one yand the same-directlon.

2. Inl a gear-hobbing machine having arotatable workpiece supporting-table, guiding means fora gear cutter supporting slide, said guiding means being` movable toward and away fromfsaid table,` and a'gear' cutter supportingslide slidable onsaid guiding means and including a cutter spindle for supporting androtatinga gear. cutter,the combination of: a Amain worm` wheell rotatably connected to said cutter spindle, two worms respectively A arranged in meshingl engagement with said maint worm wheelandtplaced.diametricallyi opposite each other, the

right and'left ilanksof each` of`said two wormshavingt a dilferenti pitch whereby the thicknessxof thevarious turns of the thread of each worm varies, two shafts re- 5 6 spectively rotatably supporting said worms, said worms References Cited in the file of this patent respectively being axially adjustable on -said shafts, a UNITED STATES PATENTS pair of auxiliary worm wheels respectively arranged for driving connection with said shafts, each of said auxiliary 1105649 Grundstem Aug 4 1914 worm wheels and the respective shaft pertaining thereto 5 111991601 Parsons et al- Sept. 26, 1916 being rotatably adjustable relative to each other to therelswzsis l Maag Nov' 6 1923 by bring about a circumferential adjustment of said 16ggg larsons et al' zug 3 worms relative to each other, and driving means common lmmermann ct to said worms and arranged to drive said worms simul- FOREIGN PATENTS taneously to thereby cause both worms to rotate said 10 554,596 Germany july 14, 1932 main worm wheel in one and the same direction. y 55,184 France Apr. 25, 1951 

